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  Should we use Abstract class or Interface?

When we write programs, we may often get into a situation where we don't know whether we should use Abstract class or Interface when we want to define an abstract object. These two are very similar and they are interchangeable in many cases. On Stackoverflow, this question is asked lots of times and it's related to many programming languages. Also in the official documentation of PHP regarding the Abstract class and Interface, people are arguing about this. To understand this question, their dif...

   DIFFERENCE,INTERFACE,ABSTRACT CLASS,COMPARISON,OOP     2013-04-15 11:44:36

  Say good bye to netbook

Asus and Acer are the last two manufacturers of netbooks, but these two companies announced that they would not manufacture netbooks starting from January 1, 2013. Prior to them, Samsung, Hewlett-Packard and Dell stopped production of the netbooks. This means that the life cycle of netbook officially ended.Back to 2009, the U.S. market research firm ABI Research was very optimistic about netbook's future, they said netbook would open a new era for PC market and predicted netbook shipments would ...

   Netbook,Tablet PC, Comparison     2013-01-02 11:53:33

  Using keytool to create certificate chain

JDK provides a command line tool -- keytool to handle key and certificate generation. This tool has a set of options which can be used to generate keys, create certificates, import keys, install certificate and export certificates etc. In this tutorial, we will show how to create certificate chain using keytool. If you want to understand how to create certificate chain programmably, please refer to Generate certificate in Java -- Certificate chain. To begin, we first generate a key pair whi...

   JAVA,KEYTOOL,CERTIFICATE CHAIN,CERTIFICATE     2015-12-17 07:09:33

  Check whether a remote server port is open on Linux

As a system administrator or network engineer or application developer, there is a need to check whether a port on remote server is open so that you can tell whether the service under check is running or not. In this post, we would cover a few methods to check whether a remote server port is open or not on Linux. telnet telnet is the most frequently used command on both Windows and Linux to check port. The simple usage for this command is  telnet [host] [port] When the port is open, the o...

   LINUX,TELNET,PORT,NC,NMAP     2017-12-23 11:45:20

  String intern in Java

In Java, == is used to compare whether two objects have the same memory location, equals() is usually used to compare whether two objects have the same time and the same state.  When comparing two strings, normally we just want to know whether they have same content, so we can choose equals(). But since String comparison is so frequently needed, Java has worked on the String class to make == workable when comparing two String literals. The String class maintains a pool of emp...

   JAVA,STRING     2016-04-10 03:35:25

  Signature sign/verification demo in Java

Digital signature is commonly used in areas where data authentication and integrity are required. It is extremely important to have signature while transferring sensitive data from one peer to other peers through network since there might be malicious applications or man-in-the-middle attacks which may alter the data along the way. Java provides some APIs to generate and verify digital signature. One important class is Signature.  When generating the signature, a private key needs to be pa...

   SECURITY,JAVA,SIGNATURE     2015-11-21 09:48:12

  Different types of keystore in Java -- JCEKS

JCEKS stands for Java Cryptography Extension KeyStore and it is an alternative keystore format for the Java platform. Storing keys in a KeyStore can be a measure to prevent your encryption keys from being exposed. Java KeyStores securely contain individual certificates and keys that can be referenced by an alias for use in a Java program. The process of storing and loading different entries in JCEKS is similar to what JKS does. So please refer to the article Different types of keystore in Java -...

   Java,KeyStore,JCEKS,Tutorial     2015-01-05 00:30:56

  Write HTML easily with Emmet and Haml

Writing HTML codes is very boring and tedious as it has many tags and it's static. One solution is to use template, filling content based on other's skeleton. One another solution is high speed writing. We can write HTML codes with Emmet and Haml. These two ways have similar functions but with different characteristics. Haml is based on Ruby, so when working on Ruby/Rails projects, we recommend to use Haml, otherwise we recommend to use Emmet. 1. Emmet Emmet is a editor plugin, the official webs...

   HTML,Emmet,Haml     2013-06-11 19:46:02

  JavaScript: Private variables

The first thing you often hear when talking about JavaScript is often “JavaScript doesn’t have visibility modifiers, hence it doesn’t support private variables”. This is only valid for 50%, because JavaScript indeed doesn’t have visibility modifiers (public, private, friend) but it has closures and function scopes. With these tools we can make variables private. Let’s take the following function: var names = ["Kenneth", "John", "Marc", "Robert"]; var lookup =...

   JavaScript,private variable,closure     2012-04-28 11:46:34

  Check file readability in Java

File operation is quite platform dependent. Although Java is a cross platform programming language, the file operation in Java is also platform dependent. The obvious evidence is the file permission check. In Java, we can call canRead(), canWrite() and canExecutable() to check whether the program can read, write or execute the file specified. However, on Windows, when we call canRead() on a File object, we may get unexpected result. Actually, on Windows, when we call canRead() on a File object, ...

   Java,Files,Readable,Check     2013-12-05 06:10:15

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